When compiling the builtins with the undefined behavior sanitizer and running testcases you end up with the following warning:
UBSan: divmodsi4.c:22:17: signed integer overflow: 2147483647 - -1 cannot be represented in type 'si_int' (aka 'long')
This can be avoided by doing the subtract in a matching unsigned variant of the type.
The same kind of pattern is found in divmoddi4.c and divmodti4.c
This was found in an out of tree target.